The Anglican church has publicly challenged the UK government's willingness to break international law over Brexit, with five archbishops in Britain joining to condemn what could be a "disastrous precedent."

In a rare step, the archbishops of Canterbury and York, the two most senior bishops in the Church of England plus their counterparts in Scotland, Wales and Ireland, have written a joint letter warning that such a step would have "enormous moral, as well as political and legal, consequences."

If the internal market bill, due to be debated by the UK's upper chamber of parliament, the House of Lords, on Oct. 19 became law, it would "profoundly affect" the relationship between the four nations of the United Kingdom, the archbishops said, the Guardian newspaper reported.

The letter is signed by Justin Welby, archbishop of Canterbury; Stephen Cottrell, archbishop of York; Mark Strange, primus of the Scottish Episcopal church; John Davies, archbishop of Wales; and John McDowell, archbishop of Armagh in Northern Ireland.

The Archbishop of Canterbury is the most senior cleric in the Church of England, but the monarch Queen Elizabeth II is the supreme governor.

The four nations in the United Kingdom are England, Scotland, Wales and Northern Ireland and some pundits have predicted that Brexit could break up Britain.

Brexit is the withdrawal of the United Kingdom from the European Union on Jan. 31, 2020. The UK continues to participate in the European Union Customs Union and European Single Market during a transition period that ends on Dec. 31..

The bishops said, "We believe this would create a disastrous precedent.

"It is particularly disturbing for all of us who feel a sense of duty and responsibility to the Good Friday (Belfast) Agreement – that international treaty on which peace and stability within and between the UK and Ireland depends ..."

The archbishops said that the UK government was preparing to breach the Northern Ireland protocol, which had been agreed to facilitate the UK's departure from the EU.

The letter said: "If carefully negotiated terms are not honored and laws can be 'legally' broken, on what foundations does our democracy stand?"

The letter was published in the Financial Times newspaper.

It came after the UK's Northern Ireland secretary, Brandon Lewis, told lawmakers in September that the proposal would allow the government to break international law in a "limited and specific way."

Because they said it breaks international law, opponents have pledged to stop or amend it.

It caused a furore, with Conservative Party pro-Brexit member of the upper house Michael Howard demanding to know how the UK could criticize Russia, China and Iran for their conduct when it was prepared to flout international law.